The invention relates to a reception device comprising a low-noise frequency converter incorporating several source antennae (or xe2x80x9cfeedsxe2x80x9d). The invention applies in particular in the reception of signals transmitted by several satellites.
The reception of signals transmitted by geostationary satellites, for example satellites relaying television transmissions, is conventionally carried out with the aid of a parabola which concentrates the received beam at its focal point. A waveguide source antenna is then placed appropriately relative to the parabola so as to couple the signal received to one or more probes which transmit it to a low-noise frequency converter. The latter carries out the conversion of the signal into intermediate frequency, the converted signal being processable by satellite demodulator and/or the decoder of the receiver.
In the case in which it is desired to aim at several closely spaced geostationary satellites, several solutions are currently used. The most obvious solution, although not the most economical, is to use as many parabola as there are satellites. Another solution, suitable for the reception of signals transmitted by two closely spaced satellites, consists in using a single parabola, but with two waveguide source antennas and two frequency converters. The parabola then points either at one of the satellites, or at a position intermediate between the two. The beams emitted by the two satellites and reflected by the parabola then converge at two distinct points. The fact that, in this case, at least one of the signals is not focused optimally, results in impaired reception. Moreover, if the satellites are closely spaced, the points of convergence of the beams are likewise closely spaced, this closeness being all the greater the smaller the parabola. The problem then arises of the side-by-side positioning of the waveguides, whose dimensions are difficult to modify. Certain products on the market undertake a merging of the extremities of the waveguides, and this impairs the quality of reception even further by increasing the coupling between the beams. Moreover, the presence of several frequency converters raises the cost of the product.
There are also xe2x80x9cparaboloidalxe2x80x9dreflectors whose role is to improve the convergence of beams originating from several satellites which are more or less closely spaced. The reflectors are then designed so as to present a substantially parabolic surface to each beam.
The situation in which a number of satellites are very closely spaced angularly is a far from exceptional situation which will become more and more frequent as the geostationary orbit becomes congested. An example of a xe2x80x9cclusterxe2x80x9d of satellites in Europe is the collection of Eutelsat satellites.
The subject of the invention is a device for receiving signals transmitted by N (N greater than 1) satellites comprising means for focusing the beams corresponding to the said signals, characterized in that it comprises several source antennas, the said antennas being printed source antennae made on a single substrate.
The use of several slot antennae printed on a substrate makes it possible to overcome the problems related to the use of waveguides.
According to a particular embodiment, the arrangement of the said antennas on the said substrate is determined by the location of the points of focusing of the said beams.
Moreover, the positioning of the antennas on the substrate is determined by the arrangement of the best points of focusing available for each beam. When installing the parabola and the antennas, it will suffice to position these reception means correctly while referring to a single satellite. The positioning in respect of the other satellites is then carried out automatically.
According to a particular embodiment, the focusing means comprise an electromagnetic lens, for example a lens of Luneburg type (hemispherical lens).
Such a lens makes it possible to obtain optimal convergence of all the beams, unlike a parabola which possesses only one true focal point.
According to another particular embodiment, the means for focusing the beams comprise a parabolic reflector. For satellites which are relatively closely spaced, one parabola can be regarded as sufficient to focus the various beams adequately. For larger angular spacings, the Luneburg type lens is more suitable.
According to a particular embodiment, the means of focusing being a parabolic reflector, a first antenna is placed at the focal point of the reflector, the other antennas being placed on one side or on the other with respect to the first antenna.
According to a particular embodiment, the antennas are slot antennas.
According to the particular embodiment, the antennas are annular-slot antennas.
This form of antenna is particularly suitable for the reception of orthogonally polarized waves having linear or circular polarizations.
According to a particular embodiment, the said device comprises at least one frequency converter made on the same substrate as the said antennas.
According to a particular embodiment, the device comprises multiplexing means which multiplex the signals received by the antennas towards a frequency converter.
Thus, a single frequency converter is required. This results in a very substantial saving in space and in components.
According to a particular embodiment, the said frequency converter is made on the same substrate as the antennas.